如何获取URL到参数的第一部分？

Question

I use Xampp. Here is my directory:

\xampp
    \htdocs
        \myweb
            index.php 
            \classes
                 autoloader.php
                 classname.php

And here is the URL:

http://localhost/myweb/classname/methodname/idNum?arg=val

And I want to get this part: (everything until index.php layer)

http://localhost/myweb

How can I do that?

Note1: $_SERVER['HTTP_HOST'] doesn't return expected thing. It just returns localhost.

Note2: I can get the whole of URL and then parse it by regex to grab expected result .. But I don't want to do that because sometimes myweb folder goes away.